| Re: [chrony-users] Isolated time domains |
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On Fri, 6 Dec 2013, Miroslav Lichvar wrote:
On Thu, Dec 05, 2013 at 10:34:22AM -0800, Bill Unruh wrote:
On Thu, 5 Dec 2013, Miroslav Lichvar wrote:
In this example I think clients running chronyd would stay together
within 1 second during whole operation even with 1024s polling
interval.
That is what I am not sure of.
Well, I tried it in the clknetsim simulator. Two chrony clients were
synchronized to a chrony server, the clients were started 512 seconds
apart and they were using the default minpoll 6 maxpoll 10 values.
The wander of the clock on the server was set by the cosine or sine
function over 1e6 seconds and the smear started 0.1e6 seconds after
the simulation start to give the clients some time to reach the poll
of 10.
How different were the time at which the polls occured on the two clients? The
main problem would come if the two clients were maximally far apart in their
poll times.
But I do admit I cannot see the difference going from 16ms to 1 sec just by
that mechanism, unless the poll times in your simulation were pretty closely
synchronized.
With the cosine smear the maximum offset between the two clients was
about 16 milliseconds. Both clients dropped poll from 10 to 6 when the
smear started. With the sine smear the maximum offset was about 2
milliseconds.
Graphs of the offset between the two clients are here:
http://mlichvar.fedorapeople.org/tmp/chrony_cos_smear.png
http://mlichvar.fedorapeople.org/tmp/chrony_sinx_smear.png
I think this could be an interesting and useful feature in chrony.
I am not sure how many people would want to follow local rather than utc.
But I guess there are people who want time islands.
--
William G. Unruh | Canadian Institute for| Tel: +1(604)822-3273
Physics&Astronomy | Advanced Research | Fax: +1(604)822-5324
UBC, Vancouver,BC | Program in Cosmology | unruh@xxxxxxxxxxxxxx
Canada V6T 1Z1 | and Gravity | www.theory.physics.ubc.ca/
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